1. Field of the Invention
The present invention relates to a method for the transmission of characters by means of the code combinations of a telegraph alphabet, particularly of the International Telegraph Alphabet No. 2 (ITA No. 2) where the characters are coordinated in a single or a multiple way to code combinations, such that the complete set of code combinations corresponds at least to a set of small letters, to a set of capital letters and to a set of digits, punctuations marks and special characters.
2. Brief Description of the Background of the Invention Including Prior Art
The International Telegraph Alphabet (ITA) No. 2 has been introduced by the international standard organization CCITT for use on international telegraph networks. This alphabet employs signal frames for transmission which comprise a start step, a five unit step group and a stop step. With the aid of the five units of the five unit step groups, thirty-two different combinations can be formed which represent a set of a corresponding number of code combinations.
On the one hand, the latin alphabet, that is, a set of letters, also called letters set, and on the other hand a set of digits, punctuation marks and special characters called figures set, are coordinated to this set of code combinations. In order to change from the letters set to the figures set, one of the code combinations is employed as the figure shift code combination and for the reverse change coorespondingly a letter shift code combination is employed. In the case of a multiple transmission of these shift code combinations no further effect is generated at the receiver.
Older teleprinting machines which employ the International Telegraph Alphabet No. 2 are provided with a keyboard where each key is coordinated both to the figures set and to the letters set. The change from one set to the other set is in each case performed by actuating of a shift key, whereby the corresponding shift code combination is emitted onto the transmission circuit. More recent teleprinting machines are frequently provided with a so-called full keyboard which comprises both a set of letter keys and a set of figure keys. Further more, in most cases one or several switching keys are provided for selection of less frequently used characters as the second meaning of the keys. In the case of such a full keyboard, transmission of a corresponding shift code combination is provided automatically for every shift from one set to another.
A teleprinting machine is known from the German Patent Application No. DE-2,640,848 which exhibits both a set of capital letters and a set of small letters. Single capital letters are called by actuation of a switching key capital/small letters. Thereby, immediately before transmission of the code combination of the letter to be transmitted a letter shift code combination is transmitted. The receiver recognizes this letter shift code combinations, switches to the set of capital letters, prints the letter transmitted as a capital letter and switches back to the set of small letters. In this way a correct capital/small letters writing is achieved with this teleprinting machine.
A further teleprinting machine is known from the European Patent Application No. EP 85936, where a set of command words is employed for shifting between up to four sets of characters. The command words are formed either from a single shift code combination or from a combination of two shift code combinations. By this all code combinations succeeding a command word are coordinated to one set of the characters until another command word follows.
The joint feature of both said teleprinting machines is the possiblility of writing in capital and small letters. In both cases the multiple transmission of the shift code combinations otherwise normally being without effect according to the International Telegraph Alphabet ITA No. 2 is used for the transmission of additional shift information. However, in both cases a full compatibility with such teleprinting machines, which can process only the conventional two sets of characters, is assured. Finally, each of the two teleprinting maschines requires additional time for transmission of texts because of the additional shift code combinations to be transmitted, which time can be considerable depending on the kind of text.